This invention relates to methods for automatically controlling the spacing of motor vehicles.
To enhance the safety of motor vehicles and drivers in present-day road traffic, in addition to using vehicle spacing traffic control systems, increased efforts are being made to assist the vehicle operator in routine procedures as well as in extraordinary situations by providing systems that automatically intervene in the control of the vehicle or of individual vehicle components. A first step in this direction has been the use of antilock braking systems (ABS) and antislip regulation (ASR) to improve the stability of the vehicle in dynamically critical situations in the direction of vehicle motion, i.e. in braking and acceleration of the vehicle. Further, use is made of so-called vehicle dynamics regulation (FDR) or stabilizing regulation (FSR) to enhance vehicle stability in dynamically critical situations in directions lateral to the direction of vehicle motion, i.e. especially in situations caused or influenced by turning of the steering wheel by the operator. An FDR system evaluates sensor data received from suitable sensors in individual vehicle components or from the vehicle as a whole and correlates them utilizing special evaluating algorithms. In this way it is possible to recognize transverse dynamically critical situations and, by applying a control to individual parameters of vehicle operation, for example the angular velocity and acceleration of the steering wheel, affect the vehicle positively in terms of the transverse dynamically critical situation.
Furthermore, arrangements for automatic distance regulation (ADR) have been developed by which the controlled vehicle automatically maintains a required safe distance from a vehicle in front. One such arrangement is disclosed in U.S. Pat. No. 5,629,851 which includes a distance sensing system, an evaluating unit, and a speed control servo device to be actuated by the evaluating unit. The distance sensing system may, for example, be a radar, lidar or electronic sensing system which scans for objects in the traffic space ahead of the vehicle. The scanning angle of the distance sensing system is chosen so that objects in adjacent traffic lanes are detected as well as objects in the same lane.
The data received by the distance sensing system are transmitted to the evaluating unit which also receives data representing the speed of the motor vehicle itself, so that the speed of the vehicle in front can be calculated. Since the safe distance to be maintained between the vehicles depends on the vehicle speed, the calculation is preferably based on a vehicle following time t.sub.f as a function of vehicle speed. If the speed of the controlled vehicle is greater than that of the vehicle in front, the following time t.sub.f decreases. If t.sub.f decreases to a predetermined valve, the evaluating unit supplies a signal to a servo device which controls the velocity of the controlled vehicle. The servo device may, for example, be the throttle flap, the fuel injection valve or the vehicle brake. This velocity control process ultimately causes the controlled motor vehicle to travel at the same speed as the motor vehicle in front.
In this process, the adjacent vehicle lanes are first checked for relevant vehicles. For example, if vehicles are detected as traveling in the opposite direction in an adjacent lane, then that lane carries traffic in the opposite direction and need not be considered. The determination of whether an object is located in the same lane or in an adjacent lane is made on the basis of a defined width for the lane containing the controlled vehicle. In addition, the evaluation unit ascertains, from the data received from the distance sensor system, the direction of lateral motion of vehicles in adjacent lanes. If a vehicle moves from an adjacent lane into the defined lane width for the lane of the controlled vehicle, the evaluating unit evaluates that object as a nearest vehicle, and regulates the controlled vehicle velocity downwardly so as to maintain the required following time t.sub.f with respect to that vehicle. Correspondingly, when the vehicle in front of the controlled vehicle departs from the defined lane width, the speed of the controlled vehicle is increased until a new vehicle is detected in the same lane, as to which the constant following time t.sub.f is then maintained.
A disadvantage of conventional methods of automatic distance control is that a very abrupt deceleration may sometimes be necessary especially in the case of a cut-in operation by another vehicle. A human motor vehicle operator, by contrast, generally drives with foresight, i.e. reacts very early to such a cut-in operation, thus reducing speed earlier, so that on the whole a continuous gradual deceleration ensures. One essential requirement for acceptance of automatic driver assistance arrangements is that they should not lead to an entirely different driving behavior.